I am wondering what the general rule is on how much a kitchen sink drain pipe should drop every 10 ft? I am relocating my kitchen and when I looked at the new 30 ft. kitchen sink/ garage disposal drain pipe under the house the total drop was only 1/2". It appears to almost sit level across the pipe span. I am afraid my kitchen sink will not drain properly and will back up if this pipe doesn't have more of a drop over the 30'.

massplumber2008

Hi mamadog:

All plumbing pipes 3 inch and smaller are required by ALL plumbing codes to have 1/4" pitch per foot of piping.

In the case of a 30 foot run of pipe from kitchen sink you would therefore require a minimum of 7.5" pitch to the pipe. This pipe should also have hangers every 4 feet.

Sounds like the new work hasn't been inspected... Also wondering what size pipe (best size is 2" pipe, but 1.5" is allowed in some areas) was run and if you will have a garbage disposal? Lastly, you should also have a full size cleanout UNDER the kitchen sink and another cleanout in the basement at any major change in direction in the piping.

Who piped this drain...? How is the sink vented??

Let me know what you can...

MARK

speedball1

Your pipe should slope 2 1/2"every ten feet for effective drainage. This works out to 7 1/2" for a 30' run at 1/4" to the foot fall. The configuration that you have almost guarantees you problems especially if you have a disposal installed. As Mark pointed out while 1 1/2" is acceptable in some areas a 2" kitchen drain is what we normally put in. For some time now our local code has mandated a 3" drain for kitchen drainage. This came about with the advent of garbage disposals. This 3" drain was extended up to become the main house vent as reguired by our code. While we don't require cleanouts it's a very good practice to install them. Would it be possible to call your installer back and have the job done correctly? Good luck, Tom